“I’m leaving it up to Reid. That’s what the caucus did yesterday. We said he would be the lead on it,” said one Democratic senator. “There was some suggestion that we would all make calls. And everybody said the best idea is to let the leader handle it.”

A senior Democratic aide said that thinking reflects an acknowledgement among the senators that Reid is the one member of the caucus who “has an actual relationship with him.”

Sanders is a political independent who caucuses with Democrats. That’s made him a bit of an outsider with his colleagues, something highlighted by the Vermont senator’s rebuke this week of a Democratic Party he says should open its doors to political independents.

The presidential candidate is not chummy with his colleagues.

Fellow senators have been known to roll their eyes at his idealistic — some say unrealistic — jeremiads in private meetings. Sanders is known for speaking out at the sessions.

Reid, however, has always been a helpful ally. He gave Sanders the full benefits of membership in the Democratic caucus after his election to the Senate in 2006, rewarding him with the committee assignments he wanted even though he was not a registered Democrat.

Reid left Tuesday’s meeting early to speak to Sanders on the phone about the caucus’s concerns. But after the two senators spoke, the Sanders campaign released a defiant statement that was more about defending its supporters and criticizing the Democratic Party than vice versa.

Yet Tuesday’s developments raise questions about the limits of Reid’s influence on Sanders, a fact Feinstein alluded to in saying that Sanders should defer to Reid.

“He is the Democratic leader of the Senate, and Sen. Sanders is a member of the Democratic caucus. He’s not a Democrat, he’s an independent — he’s really a socialist — but he’s a member of our caucus, and as such, he should listen,” Feinstein told The Hill.

Reid expected Sanders to condemn outbursts over the weekend at the Nevada convention, where the state party was meeting to allocate delegates to the presidential hopefuls.

Instead, Reid said he was “surprised” by the defiant response and dismissed it as a “silly” stunt put together by campaign staff and not representative of Sanders’s views.

But that explanation looked unlikely hours later when Sanders delivered a fiery stump speech in Southern California, hitting some of the same points and challenging the Democratic Party to change its ways and shed its dependence on big-money donors.

“The Democratic Party is going to have to make a very, very profound and important decision. It can do the right thing and open its doors and welcome into the party people who are prepared to fight for real economic and social change,” he said, eliciting roars of “Bernie or bust!” from the crowd.

Reid has some credibility as a fair broker because he stayed neutral in the primary race until after the Nevada caucuses in February, when he endorsed Clinton. Many of Sanders’s other Democratic colleagues backed the former secretary of State immediately after she announced her candidacy.

One senior aide described the dynamic between Reid and Sanders as “a really close personal relationship,” noting several similarities between the two lawmakers that may not seem obvious at first glance.

Both have strong independent streaks.

Reid is allergic to Washington’s social circuit of receptions and dinners that draw many members of Congress.

“He’s never been a creature of D.C.,” the aide said. “I can’t remember a single reception or dinner that he’s been to.”

Sanders is also something of a loner who shows little interest in hanging out with lobbyists.

A few years ago, he attended a Democratic Senatorial Campaign Committee retreat on Martha’s Vineyard, to which lobbyists and other big-money donors were invited. But instead of chatting up the other guests at Edgartown’s Harbor View Hotel in hopes of fattening party coffers, Sanders largely skipped the proceedings to enjoy the island’s attractions, according to a lobbyist who attended.

The senior aide said Reid “respects Bernie because he’s also an iconoclast and a strong voice for things he believes in.”

Another senior Democratic aide said Sanders “has been in frequent contact” with Sanders. They spoke Thursday, Friday and again on Tuesday.

Suspicion is growing among Democrats that Sanders might be setting the increasingly pugilistic tone for his campaign himself.

“The ‘burn it down’ attitude, the upping the ante, everything we saw in that statement released [Tuesday] by the campaign seems to be coming form Sanders himself. Right from the top,” wrote Josh Marshall, a prominent left-leaning journalist, who cited “multiple highly knowledgeable, highly placed people.”

Democratic senators have given Sanders a wide berth so far, treading carefully on the question of whether he should drop out of the race due to Clinton’s overwhelming delegate lead.

But patience is beginning to wear thin.

Colleagues are growing more frustrated that an independent whom they welcomed as one of their own into the caucus is now wrecking havoc in the party.